1. Field of the Invention
This invention relates to a fluid medicine delivery device, and, more particularly, the invention is directed to a microdispensing ophthalmic pump for delivering a microdose of ophthalmic fluid.
2. Description of the Prior Art
U.S. Pat. No. 5,152,435 (hereinafter xe2x80x9cthe ""435 patent)xe2x80x9d, entitled xe2x80x9cOPHTHALMIC DISPENSING PUMPxe2x80x9d, discloses a manually operated dispensing pump capable of delivering a precise quantity of ophthalmic solution to the surface of an eye in a desired spray pattern with an impact pressure on the eye that is comfortably tolerable by an individual and was issued to a co-inventor, Ben Z. Cohen, of this patent. The ""435 patent is incorporated by reference herein, including the extensive discussion of the shortcomings of the prior art. The spray pump of the ""435 patent is substantial improvement over the prior art, capable of delivering doses of ophthalmic fluid such as 50 microliters in the previously described manner. However, often a dose of much less than 50 microliters of ophthalmic fluid may be required to be delivered in the manner described above. Since a reduction in the size of a dosage inherently decreases the impact force exerted by the dose onto an eye, the administration of fluid by the ""435 patent would be even more comfortably tolerable than that disclosed therein with a reduction in the size of the dose the ""435 pump could deliver. Also, some medications can have toxic effects, even at doses as small as 50 microliters, and so doses of less than 50 microliters would be better tolerated.
It is a primary object of the subject invention to provide a manually operated microdispensing pump for delivering a microdose of ophthalmic solution as small as 5 microliters.
Also, it is an object of the subject invention to provide a manually operated microdispensing pump capable of repeatedly administering a full and proper microdose as small as 5 microliters.
The above-mentioned objects of the present invention are achieved by a new and improved manually operated microdispensing pump for delivering ophthalmic fluid. In particular, the new and improved manually operated microdispensing pump will enable an individual to repeatedly deliver a predetermined microdose of ophthalmic fluid.
In the preferred embodiment, the microdispensing pump of the subject invention is formed to be substantially cylindrical with one end being formed as a reservoir for storing the ophthalmic fluid intended to be dispensed. A pump body is threadedly secured to the reservoir with a cylindrical inner body formed therein which projects along a central axis into the reservoir. A dip tube is provided to communicate fluid from the reservoir to the inner body of the pump body. A pump mechanism is disposed within the inner body which urges fluid from the reservoir and through the pump of the subject invention. The pump mechanism comprises an inlet check valve element for regulating the flow of the fluid from the reservoir into the inner body, a cylindrical piston slidably disposed and sealingly supported within the inner body, an elongated poppet extending from the inner check valve element and through the inner body in a spatial relationship with the piston, an outlet check valve element for regulating flow of the fluid out of the inner body and a spring for urging the cylindrical piston into an upward position in contact with a head formed on the end of the support opposite the inlet check valve element.
The microdispensing pump of the subject invention further comprises a dispensing cap mounted onto the cylindrical piston and formed with an outlet chamber which communicates with the inner body, the communication therebetween being controlled by the outlet check valve element, and a slender discharge nozzle communicating the outlet chamber with the periphery of the dispensing cap. An actuator is slidably disposed adjacent the dispensing cap and substantially within the pump body.
Once primed with ophthalmic fluid within the inner body, the pump dispenses ophthalmic fluid with a downward translation of the actuator, the dispensing cap and the piston within the inner body. As the piston translates within the inner body, the volume therein is decreased with an accompanying increase in pressure of the ophthalmic fluid contained within the inner body. The check valve elements are both normally closed and contribute to the pressure build-up of the fluid. Eventually, the compressed ophthalmic solution will force the outlet check valve element open, thereby allowing fluid to enter the outlet chamber and the discharge nozzle and force out fluid previously drawn therein. The fluid is delivered in a non-aerosolized jet stream as a series of droplets. A spring is provided to urge the outlet check valve element into a closed position quickly after being forced open. The piston, having completed its downward translation, translates upward into contact with the head of the poppet due to the urging of the spring acting on the piston. As the piston comes into contact with the head of the poppet, the volume within the inner body is increased and the accompanying pressure decreased. The reduction of pressure within the inner body creates a suction effect which urges the inlet check valve element into an open position and draws fluid from the reservoir into the inner body. As pressure builds within the inner body due to the added fluid, the inlet check valve element will be urged into a closed position allowing the pump mechanism to be used again.
The new and improved manually operated microdispensing pump of the subject application uses a spring biased outlet check valve element and a limited-travel inlet check valve element to operate under the negligible pressures and strokes associated with the delivery of microdoses of fluid. In the preferred embodiment, a spring is applied to a stainless steel ball to form the outlet check valve, which is biased to a normally closed position. The suction created by the pump mechanism to draw fluid therein may affect the microdose of the pump if fluid disposed in the nozzle and the outlet chamber is drawn into the inner body due to the suction effect. During operation of the pump, the spring urges the outlet check valve element into a closed and seated position prior to suction being created in the inner body and ensures that a proper and full microdose of the ophthalmic fluid is maintained within the nozzle and the outlet chamber, unaffected by the suction effect.
An inlet check valve element is provided to regulate the flow of ophthalmic fluid into the pump of the subject invention. Since the delivery of microdoses as small as 5 microliters involves a negligible stroke of the inlet check valve element, a protrusion is disposed opposite the inlet check valve element which restricts the check valve element""s range of motion and prevents the check valve element from simply shuttling during usage. The motion of the inlet check valve element is limited so that in an open position the volume displaced by the inlet check valve element in travelling from a closed position to an open position is less than the volume of the dose being dispensed by the pump. In the preferred embodiment, this volume is the swept volume of an inlet check valve ball and is calculated by taking the product of the clearance between the inlet check valve ball and the protrusion times the cross-sectional area of the inlet check valve ball: (clearance)xc3x97[xcfx80xc3x97(radius of the ball)2]. Although a ball is preferred, any shape inlet check valve element may be used, such as a disk, with the swept volume being determined by the product of the clearance between the inlet check valve element and the protrusion times the largest cross-sectional area of the inlet check valve element measured in a plane perpendicular to the flow of fluid through the check valve. Thus, one feature of the new and improved manually operated microdispensing pump of the subject invention is a valve arrangement sensitive to the negligible strokes associated with microdosing.
Prior to initial use, the pump of the subject invention must be primed, wherein air is expelled from the pump mechanism. The pump is primed through the repeated actuation of the pump mechanism which draws fluid therein and forces air thereout. After priming, the re-introduction of air into the pump mechanism is undesired, since air pockets may be formed within the pump mechanism which may render the pump mechanism inoperative. To prevent the entrapment of air within the pump mechanism, the pump of the subject invention includes a failsafe device, a limited volume dip tube and a spherical inlet chamber which function to prevent the introduction and entrapment of air bubbles into the pump mechanism. The failsafe device comprises a ball disposed within an arcuate slotted track formed in the dispensing cap, which cooperates with an actuating block extending from the actuator. To operate the pump of the subject invention, the actuator is urged towards the dispensing cap with the actuating block coming into contact and pressing against the ball disposed within the track, which, under further urging, depresses the dispensing cap and activates the pump mechanism. If the pump were to be operated with the opening of the dip tube exposed to air entrapped within the reservoir, air could possibly be introduced into the pump mechanism. The slot of the failsafe device is formed to guide the ball out of alignment with the actuating block when the dip tube is positioned to be in communication with air trapped in the reservoir, with the ophthalmic fluid being within a predetermined range of fluid levels. Preferably, the slot is formed to allow the pump of the subject invention to operate with the nozzle discharge positioned in a range from approximately 155 to 290 degrees, going clockwise. Outside of this range, the ball will slide within the arcuate slot and prevent actuation of the subject invention pump.
To limit the entrapment of air in the pump during priming, the inlet chamber is formed to be substantially spherical to avoid the creation or entrapment of air bubbles therein. Also, during priming, as the pump is actuated with the inlet check valve element not being encompassed by ophthalmic fluid, the inlet check valve element will not provide an adequate seal against its seat and will allow fluid to freely pass the check valve element into the dip tube. This leakage, when the inlet check valve element is in a dry state, may cause an air pocket in the dip tube which prevents ophthalmic fluid from entering the pump mechanism. The air pocket will react to the actuation of the pump by rising and falling within the dip tube corresponding to the existence of suction within the pump mechanism. As a result, ophthalmic fluid is prevented from being drawn into the pump mechanism. To avoid such a problem, the dip tube of the pump of the subject invention is formed to encompass a volume less than the microdose intended to be dispensed by the pump to ensure that the inlet check valve element is submersed in ophthalmic fluid, since the inlet check valve element will not leak when encompassed by ophthalmic fluid. The dip tube has a hollow, substantially cylindric center which contains fluid from its free end to the seat of the inlet check valve element, which will be fully drawn into the pump upon a single actuation. Limiting the volume of the dip tube below the microdose of the pump ensures sufficient fluid will be drawn from the dip tube with a single actuation of the pump which will encompass the inlet check valve element and prevent the formation of an air pocket in the dip tube. Thus, another feature of the new and improved manually operated microdispensing pump of the subject invention prevents the entrapment of air within the pump mechanism.
To ensure proper operation of the pump, an annular tapered latch, formed from a resilient plastic, is provided at the base of the actuator and disposed about the inner body and pump mechanism. A corresponding annular shoulder is formed about the inner body with a top surface which comes into contact with the bottom surface of the latch with the downward translation of the actuator. The actuator can translate downward till the bottom surface of the latch is in contact with the annular shoulder without the pump dispensing any fluid. The actuator can further translate downwards, with the latch freely deforming. As the latch continues to deform, the latch generates resistance to further downward translation requiring increasing force to accomplish such translation. The increase in force will eventually build up and overcome a predetermined threshold force, which causes the latch to yield with a great reduction in resistance to even further downward translation.
To dispense fluid from the pump, a threshold force must be applied to deform the latch and exceed the yield point, thereby allowing the actuator translation into the pump body such that the pump mechanism is activated through the dispensing cap. The force needed to overcome the latch is much greater than that required to drive the piston a required stroke. Once the latch is overcome, the threshold force will cause the piston to rapidly travel its full stroke. A full and proper dose, as predetermined by the stroke of the pump mechanism, will be ensured through the elimination of a partial pump stroke. Therefore, another feature of the new and improved manually operated microdispensing pump of the subject invention is a latch for ensuring proper dosing.
Also, the translation of the dispensing cap into the pump body results in the compression of air trapped therebetween and resistance to downward translation. Vents may be provided to allow the compressed air to escape. The combination of the latch and the vents can be used to establish a threshold force needed to operate the subject invention. The quantity and the size of the vents can be manipulated to add or decrease the threshold force needed to overcome the latch.
The deformation of the latch converts the threshold force needed to deform the latch into a rapid actuation of the pump mechanism. An operator of the new and improved pump of the subject invention will not sense the point at which the latch will deform and will continue to apply the threshold force after deformation of the latch. Once deformed, the latch provides no resistance to further translation of the actuator and dispensing cap, which under the applied threshold force will rapidly move and activate the pump mechanism. This rapid activation will cause the pump mechanism to dispense fluid in a non-aerosolized jet stream as a series of droplets which will hit the desired target nearly simultaneously. As an additional feature, the rapid translation of the dispensing cap within the pump body causes the dispensing cap to strike the pump body, which limits the translation of the dispensing body, such that an audible click, tactile click, or any combination thereof, is generated. The audible or tactile click indicates to a user of the subject invention that a dose has been administered. The audible click can be avoided by padding the point of contact either on the dispensing cap or the pump body with a cushioning material, such as rubber or laminated paper.
The latch is not necessary to create a jet stream, if the pump can be actuated quickly without it. However, the latch ensures the pump mechanism will be activated with sufficient velocity to create a jet stream. Thus, yet another feature of the new and improved manually operated microdispensing pump of the subject invention is a deformable latch which ensures delivery of fluid from the pump in a jet stream.
As with all medical dispensers, precautions must be taken to prevent the introduction of foreign matter which could cause contamination of the dispenser. The spring acting against the outlet check valve element prevents the introduction of foreign matter into the pump mechanism. During fluid administration, the inner body draws fluid through the dip tube as fluid is dispensed. The drawing effect not only affects the inlet check valve element, but also the outlet check valve element. The spring urges the outlet check valve element into a seated position prior to suction being created within the inner body and prevents the drawing of contaminants into the pump through the nozzle.
Also, the dispensing cap, along with the discharge nozzle, is disposed within the actuator during non-use. In this position, the nozzle is protected from dirt and debris. The mouth of the discharge nozzle is provided with a conical rim which aids in the separation of the discharging fluid from the nozzle. The rim is encompassed by an annular depression which provides a pocket for collecting undispensed fluid. The annular depression is recessed within the dispensing cap and provides for separation of undispensed fluid from the nozzle, thereby avoiding possible blockage, and from the actuator, thereby avoiding possible gumming on the actuator of undispensed fluid which could contaminate future doses.
Although the discussion of the subject invention refers to ophthalmic solutions and administration to a person""s eye, the new and improved manually operated microdispensing pump of the subject invention can be used with any type of fluid, such as lubricants, fragrances, medications and so on, for which a microdose as small as 5 microliters may be required.
These and other features of the invention will be better understood through a study of the following detailed description of the invention and the accompanying drawings.